Militia leaders in the north-eastern Democratic Republic of Congo's Ituri region have been urged to stop fighting and back national moves to democracy.
The UN has half its DR Congo peacekeepers in Ituri
A vice-president in the transitional government, Azarias Ruberwa, described talks with militia groups in Kinshasa as "a last chance meeting for peace."
"The country is counting on you to back the transition process," he said in a speech opening the meeting on Monday.
Thousands have died in Ituri since a national peace pact was agreed last year.
The United Nations has expressed confidence that progress can be made in the region.
But speaking to the BBC, special UN representative to the DR Congo, William Swing, said a number of rebel groups were represented at the discussions, but some rebels were still not part of the process, and needed to be brought into the talks.
"We will not accept that the massacres continue," Mr Swing said.
The United Nations, which has 4,700 peacekeepers deployed in Ituri, took over last September from French-led European Union troops.
Correspondents say rebels from the region felt left out of the national peace pact, and have been pre-occupied by a more localised conflict between the Lendu and Hema ethnic groups, which has claimed about 50,000 lives since 1999.
On Friday, UN forces clashed with the predominantly Lendu Nationalist and Integrationist Front (FNI).
Earlier this year the UN fought with the mainly Hema Union of Congolese Patriots (UPC).